The stingless wasps are one of the few natural enemies of the emerald ash borer in their native Asia, so the Minnesota Department of Agriculture plans to release them Friday afternoon as part of a broader pest management plan.

Other weapons include removal of infested trees and treating trees with insecticides.

The emerald ash borer has killed millions of ash trees in other states and threatens close to 1 billion trees in Minnesota.

The metallic green beetles were discovered in St. Paul in 2009 and have spread to Minneapolis, Falcon Heights and Shoreview. They've also turned up in Winona and Houston counties of southeastern Minnesota.